Ya'll are still giving him suggestions in stead of reading.. LOL
He rented guns, he bought his gun, S&W M&Pc
RML i didn't see though if you got the 9 or the 40?
You did mention that you're a little new to shooting so the sub compacts are going to be more difficult to get on with, but not bad, just going to take some rounds down range.
Unless you've acquired a monster flinch since you first shot one i'd say there's something up with the sights that you had installed, talk to the gunsmith that put them on and tell him what you've stated here and see what he says.
I'd also find someone else that can shoot it and see what it does for them to help rule you out as the issue...